| internal/race | Package race contains helper functions for manually instrumenting code for the race detector. |
| internal/sync | Package sync provides basic synchronization primitives such as mutual exclusion locks to internal packages (including ones that depend on sync). |
| internal/synctest | Package synctest provides support for testing concurrent code. |
| runtime | Package runtime contains operations that interact with Go's runtime system, such as functions to control goroutines. |
| sync/atomic | Package atomic provides low-level atomic memory primitives useful for implementing synchronization algorithms. |
| unsafe | Package unsafe contains operations that step around the type safety of Go programs. |